Manufacturing method of free-cutting lead steel

ABSTRACT

THIS INVENTION RELATES TO A METHOD OF PRODUCING FREECUTTING LEAD STEEL COMPRISING POURING THE MOLTEN STEEL INTO A LADLE, STIRRING THE STEEL BY PASSING THEREINTO A GASEOUS MATERIAL WHICH DOES NOT HARMFULLY AFFECTED THE QUALITY OF THE STEEL, AND FEEDING A WIRE ROD OF LEAD OR A LEAD ALLOY INTO THE MOLTEN STEEL AT AN ADDING VELOCITY OF 1 TO 20 METRES PER SECOND, SAID WIRE ROD HAVING A DIAMETER OF 5-20 MM.

April 17, 1973 MASUTA OKUBO UAL 3,728,109

I MANUFACTURING METHOD'OF FREE-CUTTING LEAD STEEL Filed Sept. 29, 1970 3,728,109 MANUFACTURING METHOD OF FREE-CUTTIN LEAD STEEL Masuta Okubo and Takaho Kawawa, Kawasaki, Japan,

assignors to Nippon Kokan Kabushiki Kaisha, Kawasaki-shi, Japan Filed Sept. 29, 1970, Ser. No. 76,428

Claims priority, application Japan, Oct. 4, 1969,

Int. Cl. C21c 7/00; C22c 39/54 US. Cl. 75-51 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of producing freecutting lead steel comprising pouring the molten steel into a ladle, stirring the steel by passing thereinto a gaseous material which does not harmfully affected the quality of the steel, and feeding a wire rod of lead or a lead alloy into the molten steel at an adding velocity of 1 to 20 metres per second, said wire rod having a diameter of 5-20 mm.

RELATED APPLICATION This application is related to application Ser. No. 78,879, filed Oct. 7, 1970.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION It is known to add lead metal of a powdery type or a grainy type to a ladle at the time of tapping to add the lead metal to the stream poured from the ladle to the mould or directly to the mould. However, by such known methods, the yield of added lead is not good. This is due to, for example, the fact that the solubility of the lead is approximately 0.3 percent for the steel at a temperature of 1650 C. Also the vapor pressure of the lead is 0.5 at the temperature of 1650 C. and a part of the unmolten lead disperses into the atmosphere and turns to vapor or the like. Furthermore, the lead vapor which disperses into the atmosphere is harmful to the human body. thus creating problems of health and sanitation for the operators.

The present invention has been developed to avoid or mitigate some of these disadvantages.

SUMMARY OF THE INVENTION The present invention provides a manufacturing method of free-cutting lead steel in which a gaseous substance such as argon, nitrogen or the like which does not affect the quality of the steel is blown into the molten steel in a ladle, stirring is eflfected and then a wire rod made of lead or lead alloy with a diameter of 5-20 mm. is added at an adding velocity of 1-20 m./sec.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the present invention reference will now be made to the accompanying drawings in which:

FIG. 1 is a side view showing schematically the outline of a ladle and feeder assembly, and

FIG. 2 is a view similar to FIG. 1 showing one modification of said ladle.

3,728,109 Patented Apr. 17, 1973 ICC DESCRIPTION OF EMBODIMENTS Firstly, steel is melted in a steel-making furnace and the steel is removed after adding required alloying materials, other than lead. The steel is placed in a ladle and contains its pre-determined content of alloying materials with the exception of lead.

In the drawings, FIG. 1 shows molten steel in a ladle 2. A gas which does not affect the quality of the steel, for example, A, N, or the like is blown into the molten steel in the ladle 2 through a porous brick 1 having a high degree of porosity. Stirring of the molten steel is effected by means of the bubbles 3 of the gas. At this time, materials which have been shaped into a wire rod from lead or an alloy of lead as the main component are added at a high velocity into the ladle 2. For this purpose, wire is fed from the feeding guide 7 by means of the wire rod feeder 6, which is driven by rollers, through the guide 5 from the reel 4. The added wire rod is made molten in'the molten steel.

The velocity at which the Wire is added is important. The adding velocity varies depending upon the thickness of the wire rod. However, to obtain a uniform dispersion in the ladle, thewire rod should be added at a velocity within the range of 1-20 m./sec. and have a diameter of 5-20 mm. If an adding velocity of below 1 m./sec. is used, a sufficient amount of lead cannot be added in a short time. Also the lead lies molten on the surface of the molten steel, so that the generation of vapor increases. With a high adding-velocity of over 20 m./sec., lead segregates in the vicinity of the position where it is added, so that a uniform dispersion cannot be obtained in the molten steel in the ladle.

As just stated, the thickness of the wire rod varies depending upon the amount of the addition, but the diameter is preferably within the range of approximately 5-20 mm. When the diameter is small, the hardness of the lead fore, desirable to raise the hardness of the wire rod a little by adding such elements as Al, Si, Mn, Cr or Ni which donot affect the quality of steel.

The action of stirring the molten steel in the ladle with a gas is required for the purpose of assisting the motion of the lead wire rod itself and of dispersing the lead content uniformly into the molten steel in the ladle. In particular, the above-mentioned action is required because the solubility of the lead is 0.3 percent for the molten steel at a temperature of 1650 C. Any kind of gas can be used as long as it does not affect the quality of the steel. In general, such a gas as A, N or CCL, can be used. The velocity of the gas is related to the adding velocity of a lead wire rod. When the adding velocity is high, it is required to set the blowing velocity of the gas and the stirring velocity high. The time of blowing the gas is usually within the range of l-20 minutes in consideration of the lowering of the temperature of the molten steel or the like.

In the modification shown in FIG. 2, gas is fed into a long porous tube containing a stopper at' its lower extremity.

In this manner, according to the present invention, a wire rod is fed into a ladle at a high velocity of l-20 m./sec., so that various efifects which could not have been obtained in the prior art can be expected. These are summarized below.

(1) As the wire rod is made molten in the molten steel, because of the static pressure, the vapor generation of lead is restricted. Accordingly, the discharge to the atmosphere is small. As an example, lead at a temperature of 1650 C. maintains a vapor pressure of 0.5 so that the phenomenon of boiling does not occur even when the temperature of the lead approaches 1650 C.

the velocity of addition and also the small surface energy of the lead. This etfect is similar to that of water drops colliding with a hard surface anddispersing as corpuscles.

. The practice of the present invention will now be 'described by way of example.

Example JIS-S35CF steel was produced in a 50 ton converter. The steel made molten in the ladle contained 0.36% of C, 0.71% of Mn, 0.32% of Si, 0.021% of P, 01018% of S and 0.016% of sol. Al. Argon gas Was blown through a porous brick (diameter of 15 cm.) at the bottom of the ladle with a pressure of 2.5-3.5 Kg./cm. A lead wire rod with a diameter of 10 mm. was added at a velocity of 4.5 m./sec. 150 kg. of the lead wire rod was added over an adding time of 37 seconds. Thereafter, Ar gas was blown for 5 minutes to complete the stirring. Then, eight steel ingots of 6 tons respectively were cast and the ingot production studied. Samples were extracted from the pouring stream every three minutes for approximately thirty minutes in the process of casting and the amount of lead and oxygen analyzed. 1

Time after the start; of casting (minutes) Lead (percent) Amount of oxygen (p.p.m.)

The yield of lead is approximately 87%, which is 'remarkably higher than the 60% obtained'if added to the stream of steel being cast. Also the lead is dispersed uniforrnly in the molten steel. At the same time, the blowing gas effects purification, so that the amount of oxygen is extremely small and a purer steel is obtained.

We claim:

1. A method of producing free-cutting lead steel comprising pouring the molten steel into a ladle, stirring the steel by passing thereinto a gaseous material which does not harmfully aflect the quality of the steel, and feeding a wire rod having a diameter of 5-20 mm. and coinprising lead or a lead alloy into the molten steel at an adding velocity of 1 to 20 metres per second.

2. A method as claimed is claim 1, wherein the gaseous substance is argon or nitrogen.

3. A method as claimed in claim 1, wherein the gaseous substance is blown into the steel through the lower part of the ladle.

4. A method as claimed in claim 1, wherein the gaseous substance is blown into the steel through a porous-tube extending substantially a major part of the depth of the ladle. 1

5. A method as claimed in claim 1, where the gaseous.

substance is blown into the steel over a period of 1 to 20 minutes.

6. A method as claimed in claim 1, wherein the wire rod is fed into the molten steel over a period of time not exceeding one minute.

References Cited UNITED STATES PATENTS 2,595,292 5/1952 Reece -129 2,259,342 10/1941 Harder 75 129 2,577,837 12/1951 Zifierer 75-129 2,197,259 4/1940 Nead 75-129 3,141,767 7/1964 Funk 75 129 3,598,383 8/1971 Moore 75-51x FOREIGN PATENTS 519,572 4/1940 Great Britain 75-123 F HENRY w. TARRING 11, Primary Examiner US. 01. X.R. 

